diff --git a/packages/@aws-cdk/aws-logs/lib/log-retention-provider/index.ts b/packages/@aws-cdk/aws-logs/lib/log-retention-provider/index.ts
index 1bb38a9f3d774..183171b18f8d4 100644
--- a/packages/@aws-cdk/aws-logs/lib/log-retention-provider/index.ts
+++ b/packages/@aws-cdk/aws-logs/lib/log-retention-provider/index.ts
@@ -188,7 +188,10 @@ export async function handler(event: AWSLambda.CloudFormationCustomResourceEvent
       hostname: parsedUrl.hostname,
       path: parsedUrl.path,
       method: 'PUT',
-      headers: { 'content-type': '', 'content-length': responseBody.length },
+      headers: {
+        'content-type': '',
+        'content-length': Buffer.byteLength(responseBody, 'utf8'),
+      },
     };
 
     return new Promise((resolve, reject) => {